Clash of the worlds
by HerondaleValdez
Summary: The Mortal Instruments gang meets the Percy Jackson gang. Will they be friends or enemies? After CoLS and BoO (assuming everyone is still alive). Rated K plus for some violence. Regular pairings.
1. Chapter 1

Chapter 1: Demons

Jace Lightwood was exhausted.

He was not what you would call your normal teenage guy. For starters, he was half angel. That's right, Jace was a Shadowhunter. He had been up all night hunting demons left and right ever since Clary left last evening with his mom and and Luke. Now it was morning and he was back in his room trying to sleep when suddenly, Alec burst in there saying, "Jace! We have to go! A massive wave of demons have been spotted near Central Park and we need to go before they hurt someone!"

"Ugh," Jace exclaimed, "can't they come back tomorrow? I need my beauty sleep!"

"Come on Jace, if we leave now, we can skip Izzy's breakfast! You know she won't let you skip it otherwise!" Alec countered.

Jace suddenly perked up and said, "What are you waiting around for, Alec, we should leave before those blasted demons hurt anybody!" Alec just shook his head and exited the room with Jace behind him.

-Line Break-

Jace, Izzy, and Alec quickly arrived in Central Park ready to fight some demons, but what they weren't expecting were four teenagers fighting some weird looking creatures that definitely weren't demons.

**A/N: Sorry I know it's short but it's just a prologue and next chapter will be in Camp Half-Blood. This is my first fanfiction so I would appreciate constructive criticism.**


	2. Chapter 2

Chapter 2: Monsters

It was a normal day at Camp Half-Blood. Well, as normal as it gets here. The Stolls were pranking, the Hephaestus cabin was working, and everyone was doing their own thing. Everything was perfect; too perfect.

All day Percy had been having this feeling that something bad was going to happen. Perhaps it would be something like a new prophecy or a new camper, but maybe a god will decided that they are angry with him and blast Percy to bits. You can never know what's going to happen when you live in a world of gods and monsters. He was walking with Annabeth when Piper walked up to them and said, "Hey guys! Chiron wants to see us in the Big House. Wonder what he wants." Piper was here at camp with Leo. Jason, her boyfriend, had gone back to check on Camp Jupiter with Frank and Hazel. There had been talk of merging the two camps, but nothing was sure yet.

"Well, you know Chiron. He usually only tells one person this important information, and that person is mostly Annabeth," I answered.

"Come on Percy, are you still angry that I didn't tell you the first Great Prophecy? I thought you were over that," Annabeth started, "I have no idea what Chiron wants, we should get going, it might be an emergency." With that being said, the three of them went towards the Big House and found Chiron and Leo in the porch.

"Ahh hello children. You four will go on a quick mission. I have already explained to Leo what's going on. You see, there was a lot of monsters spotted in Central Park and they are attracting some attention from the mortals, after all there are some things not even the mist can hide. That's why I need you four to go to Central Park and dispose of those monsters," Chiron explained.

-Line Break-

The four half-bloods finally got to Central Park and were really surprised at what they found there. There were easily more than 20 powerful monsters that were just standing there, not doing anything. That is, until they noticed the demigods. _Well, we're dead,_ Percy thought while the monsters charged at them.

The four of them burst into battle, vaporizing any monster that came near them. They were a good team, but soon enough, they started to tire. Percy's sword slashes were getting slower and slower, and when a particular feisty empousa came barreling towards him, he felt his spirit shatter. There were too many monsters and not enough demigods. Just when the empousa was about to strike his chest, a very curious looking sword hit her in the stomach and the monster went from being a scary vampire, to being golden dust.

Percy looked up to see a very determined boy with golden hair and golden eyes looking at him in a mix of confusion and persistence. "Well then, I believe that you owe me a favor, after all, I just saved your life," said the boy with the golden hair.

"Yeah, sure, whatever you say, blondie," Percy countered, "But right now I'm occupied so if you would move out of the way before a monster charges at us, I would really appreciate that."

As soon as Percy said that, a huge shadow appeared on top of him. He slowly turned around to find himself face to face to a weird serpent-like creature. "Umm, Annabeth? What is this?" he asked.

"That, Percy, would be the Python. You might want to run, the monster was slain by Apollo when he took possession of the Oracle of Delphi," informed Annabeth.

Suddenly, an arrogant voice cut into the conversation, "Run from a fight? What are you, cowards?" It was the golden boy. Suddenly, he jumped up and tried to hit the monster with his weird sword, missing. The Python then struck and missed the boy's leg by an inch. Percy tried to shout to him to come back, but it was useless, his voice wouldn't work. He tried to turn towards Annabeth, but he realized she wasn't there, she had turned invisible. He had just turned his head back to the fight when he saw the Python fall forward, dead, with Annabeth holding its head.

"Hey boy, next time don't be stupid and wait for until you're sure someone will help you. This time you got lucky," Annabeth told the boy.

"Well, sorry for saving you. I guess next time I will just let you die," he said sarcastically. "Anyway, the fight is finished and all the strange demons are gone, so why don't we celebrate?" he finished.

Percy turned around and realized he was right, the monsters were either gone or turned to golden dust. All his friends seemed to be okay with no major injuries. He was glad for that. He also realized there was a group of people, all in black clothes, moving towards them. Probably the boy's friends. "Who are you?" Percy asked.

"Why, you don't know me?" he asked, feigning mock surprise, "I'm the great Jace Lightwood and these are my friends, Alec and Isabelle Lightwood. Now, may I have the pleasure to know who I just saved and what kind of demons those were that I killed?" he continued.

"Well, what a great choice of friends you have, Jackson," Leo said annoyingly, "Not only is he arrogant and sarcastic, but he doesn't know a monster when he sees it."

"He's not my friend. And first of all, _Jace_, my friend is right, those are not demons, they are monsters. And well, as you probably heard, my name is Percy Jackson, this is my girlfriend, Annabeth Chase, and my friends Piper McLean and Leo Valdez," Percy answered.

"Well, nice to meet you guys, but we really should get going. Jace here gets a little cranky when he doesn't get a good night's sleep, don't you Jace?" Alec said accusingly.

"Nonsense, Alec," Jace countered, "we should all go to Taki's and talk about our great fight, right guys?"

"Umm, what's Taki's?" Piper spoke for the first time.

"It's this really great restaurant where you can order great food. Come we'll take you there," Isabelle volunteered.

"Sure why not?" Percy said, "Lead the way, Isabelle."

"Let's go! Oh, and by the way, I prefer Izzy." With that being said, they all good off to Taki's together, oblivious to the trouble they just brought upon themselves at deciding to travel together.

**A/N**

**Sorry sorry sorry for not updating sooner I've been busy so I kind of forgot this story. I'll now try to write every week and even if I don't post every week, I will try to advance my story. Hope you like the chapter! Remember I accept constructive criticism.**

**So, I hope you all had a good halloween! See you next time!**


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